Giyu Tomioka also known as "The Water Hashira" is a young man that has blue eyes, black hair and wears a checkered Kimono. Giyu is in the alignment of good and his goal much like every other Hashira wants to kill demons siding with most thay all demons should perish.
As a child he grew up as a happy individual who lived with his sister and mother at that time but after his sister got killed by a demon, he was traumatized and tries to tell locals of his encounter. But none believed him and instead sent him away leaving him all by himself as he ran away from home and the village until he could no longer go on.
He was founded by urodaki, the main water hashira and took him under his wing along with a friend he made some time ago, sabito. After years of bonding and training together they were countered in final selection, Giyu survived but sabito didn't make it leaving Giyu to develop a defense mechanism to prevent himself from being open or getting others killed.
so what would happen if he joined the loki familia?
Well, Because of his experience as a fighter Giyu is a very skilled swordman's who uses water breathing as his very own form. Given his past experiences he wouldn't really open himself up alot due to keeping those secrecy. If he were to interact with members of the familia he would greet them and not really as much talk through each meeting but he would offer little but encouraging words to those who either train or strive to survive.
For friends he would get along with riveria and Ais due to their stoic but quite nature. Bete would remind him too much of sanemi, Finn to him would he like a leader similar to gyomei. Foe the the rest of the weaker levels he would know them for a while until certain they would survive.
As for the dungeon, Giyu would kill all monsters testing his skills and strategy to beat. Tough monsters such as minotaurs and orcs will be no trouble for him, given his speed, strength and focus. He has 11 Water Breathing forms in those techniques that'll help him through the dungeon.
In a way he would somewhat be a trainer to those who test their strength and skills implying to even the higher levels within the familia. But also have his own business to conduct on his own purpose due to his reputation as a monster slayer.
What do you think? if Giyu was one of the loki members?